Mat, Two things, I would take Nakedanvil's advice and get the whole thing hot before the initial welding. I got in a hurry hardsurfacing an anvil without preheat and got a nice crack. Ideally a firebrick wall around it heated with propane till carbon doesnt't stick to the surface of the joint. Not having that many firebrick I would probably cut the ends out of an oil drum and place it over the anvil and fill it with charcoal and wood. It would take 2 people to get the hot drum off after the fire died down. the second is that you will need an good contact between the top and the base. Any space at all will give you a hollow anvil. Its a bad feel. I would spread some rouge compound on the two pieces and rub them around on each other then examine the contact surface. If there are any high points knock them off before going further. I would actually weight the top down while doing the tack. Good Luck, Russfelix